Inversion of GPS velocity and seismicity data to yield changes in stress in the Japanese Islands

SUMMARY To estimate stress changes within the crust from observed displacement rates, we have devised a new stress inversion method for a 2‐D plate subjected to a planar stress which uses Airy's stress function. The merits of this stress inversion method are that it allows us to estimate the stress field without full knowledge of the elastic properties of the object and it improves precision because it is not necessary to take derivatives of observed quantities. We applied this stress inversion method to the Japanese Islands where the Geographical Survey Institute has been operating a nationwide GPS array called ‘GEONET’. We make the assumption that the inelastic deformation in the Japanese Islands has no dilatational component. We used velocity data derived from 3 yr of GPS observations. We estimated the change in boundary traction from the seismic parameters of large earthquakes (stress drop, slip direction and recurrence interval). We compared the observed ‘total’ strain and estimated the ‘elastic’ strain. The results suggest that the latter looks larger than the former, indicating that it is feasible to estimate the distribution of rigidity from the stress inversion. Comparison with seismicity data suggests that inland shallow earthquakes occur where rigidity is lower.